Many devices are known which create a swirling air pattern within a totally or near totally confining enclosure. Prominent among such prior art devices is the Ranque Tube refrigeration unit examplified in U.S. Pat. No. 1,952,281 issued Mar. 27, 1934 to G. J. Ranque. This patent discloses a variety of tubular elements comprising walls which completely surround the pattern area. A fluid under pressure is forcibly introduced tangentially into the tubular element so as to swirl therein and to produce two coaxial sheets of fluid. The outer sheet is compressed against the confining wall by expansive forces of the inner sheet, the compression absorbing a certain amount of work. The absorption of work is evidenced by a rise in temperature of the compressed sheet at the expense of the other sheet, which is thus cooled. Fluid extracted from the respective sheets is thus useful as hot and cold fluids.
In another prior art disclosure, namely U.S. Pat. No. 3,266,466 issued Aug. 16, 1966 to Eugene Fehr, a swirling pattern of combustion products is produced by introducing the entirety of a confined flow into a tubular conduit comprising walls which virtually totally enclosed the pattern area, i.e., including an opening only sufficient to introduce the combustion products through a restrictively confined flow path. Again, the creation and maintenance of the swirling pattern depends upon the confinement of the tubular wall which inherently imposes a viscous drag against the rotational motion of the gas. In order to maintain a consistent swirling pattern throughout the pattern area, it is necessary to match the wall radius to the pressure gradient formed as the gas progresses axially of the tubular conduit, a condition that will persist only at a given set of conditions of mass velocity of incoming and exiting combustion products. Otherwise, the flow through the tubular conduit rapidly becomes predominently an axial flow with the rotational vector diminishing or completely ceasing.
Other prior art relating to combustion chambers reveals toroidal or annular patterns of whirling fuel/air mixture created within the confining walls of the combustion chamber. See, for instance, U.S. Pat. No. 3,030,733 to R. H. Johnston and U.S. Pat. No. 3,007,310 to K. Eisele. In this prior art, the swirling motion is imparted by flow directing elements which depend again upon a high velocity entering flow and confinement by chamber walls, and are operative only under certain pre-established conditions of flow rate.
Other prior art exemplified by U.S. Pat. No. 2,894,703 issued July 14, 1959 to D. C. Hazen et al and U.S. Pat. No. 3,396,738 to G. Heskestad discloses structures in which a flow is initiated along a restrictive surface in a direction approaching a discontinuity in that surface. The presence of the restrictive surface causes the gas passing therealong to assume a laminar pattern as a result of the boundary layer phenomena. The laminar pattern is characterized by a pressure gradient which decreases with distance away from the surface approaching the discontinuity. Hence, when passing over the discontinuity, the pressure gradient is the opposite of what is desirable in establishing a stable vortex downstream of the discontinuity. At this point, both Hazen et al and Heskestad create a low pressure area adjacent the high pressure side of the laminar stream in an attempt to reverse the pressure gradient across the stream. The result is ineffective to create a smooth stable vortex, the gas entrained from the low pressure area of the laminar stream becoming turbulent, a condition counter-conducive to a stable vortex. Note that both Hazen and Heskestad find it desirable in some embodiments to exhaust gas from this turbulent area. Moreover, Hazen discloses an outer flow-directing wall which completely encircles the vortex area 40, constraining the flow completely around the circumference to the point of reentry into and entrainment with the entering air stream.